The present invention relates generally to a mixed source growth apparatus which is particularly suitable for preparation of Group III nitride ultraviolet emitters.
Group III nitride compound semiconductors such as, for instance, gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN) (hereinafter also referred to as a “Group III-nitride semiconductor” or “III-nitrides”) have been gaining attention as a material for semiconductor devices that emit green, blue or ultraviolet light. A light-emitting diode or a laser diode that emits blue light may be used for displays, for lighting and for high-density optical disk devices. A light-emitting device (which together with the acronym LED, when used herein, will for convenience also refer to both a light-emitting diode and laser diode unless otherwise specified) that emits ultraviolet radiation is expected to find applications in the field of ultraviolet curing, phototherapy, water and air purification, bio-detection, and germicidal treatment. The ultraviolet portion of the electromagnetic spectrum is often subdivided by wavelength into UVA (315-380 nm), UVB (280-315 nm) and UVC (<280 nm).
Group III nitride semiconductors are typically manufactured by incorporation of vapor phase reactants in a reaction chamber. Particularly suitable techniques include Hydride Vapor Phase Epitaxy (HVPE) and Metal-Organic Chemical Vapor phase Epitaxy (MOCVD) both of which are well known in the art.
HVPE is a favored technique for GaN deposition. It provides relatively rapid growth in a cost-effective manner. In HVPE growth of GaN proceeds due to the high temperature, vapor-phase reaction between gallium chloride and ammonia. GaCl is typically produced by passing HCl over a heated liquid gallium supply. The two gases are directed towards a heated substrate and reaction occurs to produce solid GaN on the substrate surface.
With MOCVD growth a nitrogen source, such as ammonia gas, is reacted with metallo-organic compounds at high temperatures above or on a substrate leading to deposition of a solid semiconductor
HVPE and MOCVD are complementary techniques which are not totally compatible. There has been some desire to utilize both techniques during the layer build up in an LED but the incompatibility has made this task difficult. One method for incorporating both techniques includes the transfer of material from an HVPE device to a MOCVD device between subsequent steps. This requires the materials to be maintained in a clean area during transfer, which is cumbersome, and greatly complicates manufacturing.
There have been some efforts to form a hybrid system wherein components of a HVPE device and components of a MOCVD device are merged into a single reactor. This technique is exemplified in U.S. Pat. No. 6,569,765. While advantageous, this system has significant limitations which have prohibited its widespread use. In particular, particle free and pre-reaction free III-nitride layers are difficult to prepare in such a device. A further problem is that pulse atomic layer epitaxy growth are not easily accomplished due to the complexity associated with flow control through the various interlinked reactor supply vessels.
Incorporation of aluminum is particularly difficult. HVPE growth requires a high temperature. The reaction vessels employed are quartz which can react violently with aluminum at the usual temperatures employed. Therefore, with a design as detailed in U.S. Pat. No. 6,569,765 it is very difficult, if not impossible, to incorporate aluminum.
Efforts to thermally segment the reaction chamber have met with limited success. To have any significant temperature gradient the zones must be sufficiently separated to allow control. It is very difficult to have thermal zones without some cool zones. The cool zones cause condensation which is undesirable.
There has been an ongoing desire for a single apparatus wherein HVPE and MOCVD growth can occur on a substrate simultaneously, or sequentially, without the substrate being removed, without premature precipitation and without the risk of unintended reactions or reactions which are not advantageous.